Rewilding the Sea - Feral: Rewilding the Land, the Sea, and Human Life - page 239

the mammoth steppes of Beringia, which, as the grass grew longer
and its detritus insulated the soil, turned to mossy tundra when the
grazing animals were killed (see chap. 6).
Perhaps the most famous trophic cascade in the seas took place
along the eastern rim of the Pacific, where sea otters, once widespread
and abundant, were almost wiped out by both native people and fur
traders. The result was the near-disappearance of the coastal ecosys-
tem. Sea otters prey on urchins among other species. Sea urchins graze
on kelp, the long and leathery seaweed that, in the right conditions,
produces tall, dense growths reminiscent of terrestrial forests. These
harbour a wonderful variety of fish and other creatures. When the sea
otters were killed, the urchins wiped out the kelp forests, bringing
down the rest of the natural system. 29 In the few places in which the
otters have survived and begun once more to proliferate, the kelp
forests have started to return, just as the reintroduction of wolves to
the Yellowstone National Park has permitted the trees to grow back.
But now, in one of their remaining strongholds, the Aleutian archipel-
ago, the sea otters are disappearing again, apparently because of
another disruption of the ecosystem. Killer whales, deprived by human
hunters of the seals and sealions they once preyed upon, have started
eating the otters instead. 30
Fishing has transformed the life of seas everywhere, to a much
greater extent than most people know. As on land, no removal of an
abundant species is without consequences, consequences that often
ramify through the system. Take the humble oyster. I have mentioned
the remarkable abundance of oysters on the eastern seaboard of the
Americas that the first European adventurers encountered. It appears
that similar concentrations were once found in other seas. A map
made in 1883, 500 years after trawling began there, marks an area of
the North Sea the size (inevitably) of Wales as oyster reef. 31 Before the
age of trawling and dredging, it is possible that most of the North Sea
bed was encrusted with oysters, while shellfish of other species would
have colonized the sediments on which oysters could not settle.
One result is that this grey sea might once have been clear. Like
most two-shelled molluscs, oysters filter the seawater. They also sta-
bilize the sediments of the seabed. Less mud would have been raised,
and that which was washed into the water would quickly have been